Attitude control system design for unmanned aerial vehicles using H-Infinity and loop-shaping methods

The aim of this paper is to design a helicopter attitude control system with guaranteed performance that allows tracking control of all three attitudes- roll, pitch, and yaw, while preserving a structure that is generally accepted in the helicopter control community. The paper presents an approach for designing compensators for shaping the closed-loop attitude step response using H-Infinity output-feedback design techniques. Simplified conditions are used which only require the solution of two coupled matrix design equations. The problem of stabilization of the angular position vector of an autonomous rotorcraft platform in a hover configuration is addressed. This paper extends previous designs by giving an H-Infinity design for a tracking controller for all three attitude states. In previous work, only two attitudes were commanded, namely roll and pitch. This paper thereby lays the foundation for future work in closing an outer control loop for hover and station-keeping control of UAV helicopters. The rotorcraft model is first loop shaped to achieve desired characteristics about the hover operating condition. A numerically efficient solution algorithm to solve the H-Infinity coupled design equations is used. A major contribution is that an initial stabilizing gain is not needed. The efficacy of the control law and the disturbance accommodation properties are shown on a rotorcraft design example.